A student investigated the relationship between current / and potential difference V for a filament bulb - Leaving Cert Physics - Question 4 - 2017

Plot the data provided in a graph with:

• Voltage (V) on the x-axis
• Current (I, in mA) on the y-axis. Label the axes appropriately and plot each pair of values accurately. Ensure a good fit to the graph.

1. To calculate resistance (R), use the formula: $R = \frac{V}{I}$
   • For 0.5 V, find the corresponding current from the graph, then compute: $R = \frac{0.5}{0.011} \approx 45.45 \Omega$
   • For 8.5 V, find the current (around 70 mA) to calculate: $R = \frac{8.5}{0.070} \approx 121.43 \Omega$

The resistance of the filament begins to change significantly at around 4.0 V to 6.0 V, where the graph starts to curve.

The resistance of a filament changes with its potential difference due to the following reasons:

• As potential difference increases, current increases, which leads to an increase in temperature of the filament.
• As the temperature rises, the resistance of the filament also increases due to the nature of the materials involved.